The present invention relates to a spatial light modulation device which converts an incoherent optical image into a coherent optical image, and is applicable to, e.g., parallel, coherent optical information processing.
Conventional light modulation devices utilize a phenomenon that a phase difference between the ordinary ray and extraordinary ray passing through an electro-optic crystal, which is caused by its birefringence, is changed by a voltage across the crystal, and their input/output characteristic (i.e., Y-characteristic) is changed by choosing between the normal mode and the hard clip mode. In writing an optical image in the normal mode, the voltage of the back surface of the electro-optic crystal is set such that the voltage of its front surface does not become negative, and the back surface voltage is abruptly decreased like a step function. In the hard clip mode, on the other hand, the back surface voltage is set such that the front surface voltage can take a negative value, and the back surface voltage is ramped down.
Therefore, conventional devices can only choose, as the input/output characteristic, one of the linear (i.e., sin.sup.2) characteristic of the normal mode and the thresholding characteristic of the hard clip mode. This causes a problem that the image processing cannot be performed while arbitrarily selecting the grey scale.
Conventional devices encounter another problem when they are used as units in a neural network. That is, because of their narrow range in selecting the input/output characteristic, it is difficult to adjust the time to be taken until a network is stabilized.